Vehicle windshields typically include a pair of bent glass substrates laminated together via a polymer interlayer such as polyvinyl butyral (PVB). It is known that one of the two glass substrates may have a coating (e.g., low-E coating) thereon for solar control purposes such as reflecting IR and/or UV radiation, so that the vehicle interior can be more comfortable in certain weather conditions.
Conventional windshields are made as follows. First and second flat glass substrates are provided, one of them having a low-E coating sputtered thereon. The pair of glass substrates are washed and booked together (i.e., stacked on one another), and then while booked are heat bent together into the desired windshield shape at a high temperature(s) (e.g., 8 minutes at about 600–625 degrees C.). The two bent glass substrates are then laminated together via the polymer interlayer to form the vehicle windshield.
Unfortunately, yields for such windshields are often as low as 70% (i.e,. up to 30% may have to be thrown out). These rather low yields are caused by a number of factors, some of which are now described.
The glass substrates are typically made by the known float process which is very efficient and effective. During the glass making process, SO2 is often used and tends to collect on the non-tin side of the glass. The presence of SO2 deposits at the glass surface is not an immediate problem, but upon heat treatment (HT) at the high glass bending temperatures mentioned above the presence of this material can cause blemishes or imperfections (e.g., sometimes known as fish-eyes) to appear in the final vehicle windshield. Other undesirable surface deposits which can occur on the glass surface and which may ultimately cause significant blemishes or imperfections in a resulting windshield include: suction cup marks made during handling, grease pencil marks, glove marks, spray paint marks, scratch(es), thin film(s) of impurities, stains, oil/grease, and/or the like. Again, one or more of these undesirable deposits can result in windshield blemish(es) which may cause the windshield to have to be thrown away thereby resulting in low yields at a significant cost to the windshield manufacturer.
In view of the above, a need in the art exists for improving yields in vehicle windshield production and/or reducing the occurrence of significant blemishes in vehicle windshields (e.g. fish-eyes). It is an object of certain embodiments of this invention to fulfill one or more of these needs, and/or other needs which may become apparent to the skilled artisan from the description herein.